1) Field of the Invention
The present invention relates to a method for controlling power supply to prevent counter-electromotive voltage due to an inrush current passing through a fixing heater embedded in a fixing roller of an image forming apparatus, such as a digital copying machine.
2) Description of the Related Art
Japanese Patent Application Laid Open (JP-A) No. 2002-184554, JP-A No. 2003-295659, and JP-A No. 2003-297526 disclose technology for a heating element (fixing heater) of a fixing device used in an electrophotographic image forming apparatus. This technology is such that in addition to a power supply from a commercial power supply, a chargeable auxiliary power supply using an electric double layer capacitor is used to allow fast rising of temperature and thereby enhance effects of power saving.
In the conventional technology, however, if power is supplied from a capacitor to the heating element when the heating element is not heated, a large inrush current passes through the heating element, and counter-electromotive force may occur caused by an inductance component of the heating element. A circuit may be broken by voltage breakdown. To solve such inconvenience, it is desirable to use both a semiconductor switch and a mechanical switch as a switching element for controlling on/off of discharging from the capacitor to the heating element.